Disengageable nut and screw arrangement

ABSTRACT

A nut and screw arrangement particularly for scientific instruments having a lead nut and screw in which the nut has two bores inclined with one another, the one plain and the other screw threaded and means for tilting the nut into and out of engagement of the lead screw so that part of the apparatus may be advanced finely by the screw and coarsely manually.

Waited States Patent Taylor I 1 Sept. ll, 1973 DISENGAGEABLE NUT ANDSCREW [56] References Cited ,7 a UNITED STATES PATENTS [75] Inventor:Peter Graham Taylor, Cambridge, 1,589,307 6/1926 Svebilius 74/424.8 AEngland 2,261,537 11/1941 Zamarra 74/424.8 A 2,430,458 11/1947 Farrell74/424.8 A l 3,049,807 8/1962 Smeets 33/165 [73] ASslgnee. giafihe z gasg gg g'zggga 3,535,793 10 1970 Williams et al. 33/165 [22] Filed; Sum30 1971 Primary Examiner-Charles J. Myhre Assistant Examiner-Wesley S.Ratliff, Jr. PP N05 185,258 AttorneyWigman & Cohen [30] ForeignApplication Priority Data [57] ABSTRACT Sept. 30, 1970 Great Britain46,617/70 I A nut and screw arrangement particularly for scientific 52us. Cl 74/s9.1s 33/165 74/424.:; A instruments having a lead nut andscrew in which the 511 Im. Cl. .1 Fl6h 27/02 has ihchhed with the One[58] Field of Search 74/89.l5 424.8 A- Plain and the other Screwthreaded ahd meahs ing the nut into and out of engagement of the leadscrew so that part of the apparatus may be advanced finely by the screwand coarsely manually.

3 Claims, 15 Drawing Figures Pakented Sept. 11, 1973 I 3,757,591

6 Sheets-Sheet 1 FIGQ. FIG. [0.

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AT TO R NEYS Patented Sept; H, 1973 6 Sheets-Sheet 4 |NVENTOR BP$TERGRAHAM TAYLUR 7am Minnow- ATTORNEYS atented Sept. H, 1973 6 Sheets-Sheet5 INVENTOR PETER GRAHAM TAYLOR BY Wm, /gwM-I MQ ATTORNE P Patented Sept.11,1973 3,757,591

6 Sheets-Sheet 6 illlllillllllIIIIIIIIIIIHIIIIIINEW INVENTOR PETERGRAHAM TAYLUR BY *7 flaw J .mm a I; ATTORTNEYS DISENGAGEABLE NUT ANDSCREW ARRANGEMENT The invention relates to a disengageable nut and screwarrangement, and particularly, but not exclusively, to a disengageablenut and lead screw arrangement for scientific instruments.

In the conventional nut and screw arrangement where, for example, atravelling microscope on parallel support bars is caused to move acrossa support base by means of the rotation of a lead screw engaging anonrotatable nut on the microscope, it is essential for one to rotatethe lead screw within the nut to move the microscope from every point toevery point within the range of movement. This is a time consumingprocedure when the position of the microscope has to be changed someconsiderable degree, and it is the object of the invention to provide adisengageable nut and screw arrangement in which the nut can bedisengaged from the screw and moved quickly from one place to anotherand then re-engaged.

The invention consists in a nut and screw arrangement in which there isa longitudinal aperture through the nut which in part comprises a screwthreaded bore which is of such dimensions that it will co-operate withthe thread upon the screw, characterized in that the nut in partcomprises a plain cylindrical bore which is of such dimensions as willform a sliding fit upon the thread of the screw, the axis of the screwthreaded bore and the axis of the plain cylindrical bore cutting oneanother at an angle, and having means for varying the relative positionof the two axes so that when the axis of the screw is positioned suchthat it coincides with the axis of the screw threaded bore the thread onthe two members engage, and when the'axis of the screw is positionedsuch that it coincides with the axis of the plain cylindrical bore, thetwo members may slide freely relative to one another.

The invention further consists in a nut and screw arrangement as setforth in the preceding paragraph in which the point at which the saidaxes cut one another is intermediate the ends of the nut.

The invention still further consists in a nut and screw arrangement asset forth in the preceding paragraph in which the point at which thesaid axes cut one another is halfway between the ends of the nut.

The invention still further consists in a scientific instrument having apart moveable relative to another part to adjust the instrument for use,characterized in incorporating a nut and screw arrangement as set forthabove, for adjusting the relative movements of said parts either finelyor coarsely as desired.

The accompanying drawings show, by way of example only, severalembodiments of the invention, in which,

FIG. 1 shows diagrammatically a travelling microscope the position ofwhich is varied progressively by a nut and screw arrangement, and inwhich the nut is disengageable from the thread of the screw inaccordance with the invention.

FIG. 2 is a part longitudinal section part elevation of I FIG. 6 is adetail showing a nut with a part spherical end,

FIGS. 7 and 8 show in elevation two views of a further nut and screwarrangement with rotatable tilting means for the nut,

FIGS. 9 and 10 show diagrammatically the effect of the choice of threadand choice of point of cutting of axes respectively,

FIG. 11 is a perspective view of a sledge microtome incorporating a nutand screw arrangement constructed in accordance with the presentinvention,

FIG. 12 is a longitudinal section of the sledge portion of theinstrument of FIG. 11,

FIG. 13 is an inverted plan view of the body portion of the instrumentof FIG. 11,

FIG. 14 is a cross section of the instrument on the line 14-14 of FIG.12, while FIG. 15 is an end elevation of the sledge portion.

FIG. 1 shows diagrammatically a typical arrangement of a travellingmicroscope 1 constrained to follow a rectilinear path across thespecimen 2 by contacting guide rails 3 supported upon end members 4 upona base 5. The microscope 1 is provided with a nut 6 constructed inaccordance with the invention, which cooperates with a lead screw '7rotatable by means of a calibrated drum'8 attached thereto. When the nut6 is in the position as shown in the figure the microscope movesprogressively either way by rotating the drum. By tilting the nut 6relative to the lead screw 7 the threads on the two members becomedisengaged, and the microscope may be slid to a new position directlywithout rotating the drum 8 and then re-engage'd for microscopicmovement of the instrument.

In one form of construction the microscope is supported upon the nut andthe nut rests against the guide rails 3 to prevent it turning. When themicroscope l is tilted by hand the nut is tilted, and the threads becomedisengaged. How this is effected is clearly seen from FIGS. 2, 3 and 4.The nut 6 is firstly provided with an axial screw threaded bore 9 whichco-operates with the thread 10 on the lead screw 7. It is then tiltedthrough an angle which can vary depending upon the nature of the threadand the position of the point of intersection of the axes, and a plainbore ll is made which is a sliding fit upon the thread of the leadscrew. FIGS. 3 and 4 are end elevations of the left and right ends ofthe nut 6 respectively as viewed in FIG. 2. V v

FIG. Sshows the application of the invention to a jack like'form ofconstruction in which the load is applied vertically downwards tothe'rotatable member 12 which has a stepped portion 13. In the figuresthe load is applied by the stepped portion 13 to the side of the nutwhich causes engagement of the screw threads as shown. When therotatable member 12 is rotated the nut is tilted so that the threadsbecome disengaged. In practice the rotatable member is firstly rotatedto the disengaged position, in which the weight of the rotatable member12 keeps the nut tilted. The nut is then lifted by hand until engagementis made with the load. The rotatable member is then rotated 18 to engagethe threads and the load is lifted by rotating the screw.

When it is desired to avoid the tendency of the load to tilt the nuteither one way or the other, the nut may be formed with a part sphericalprojection 14, see FIG.

6, which fits in a part spherical recess 15 in a loaded member, thecenter of the sphere being concentric with the point of cutting of theaxes of the screw threaded part of the bore with the plain part of thebore. Further more, in this construction the effect of tilting the nutdoes not impart any longitudinal movement of the loaded member.

In the construction shown in FIGS. 7 and 8 the nut 6 is provided withprojection 17 which engages with V shaped recesses 18 in the loadedmember 16. In this case the load acts to tilt the nut to causedisengagement of the screw threads.

If in the construction shown in FIG. 8 the projection 17 is repositionedas shown by the dotted lines, when in this case the load acts to tiltthe nut to cause disengagement of the screw thread.

In general, the nut can be of any convenient shape or size, dependingupon its application. For instance, a square holed nut using strips ofrack could be used, but owing to the line contact between the lead screwthread and the rack the rate of wear would be excessive.

The device makes use of the increasing clearance between the matingthreads as the nut is tilted about the point of intersection of the axisof the lead screw with the axis of the plain bore, and in consequencethe dimension R1 must be greater than R2. See FIGS. 9 and 10. The angleof the teeth may be varied but R2 must not exceed R1.

The effect of moving the point of cutting of the axes to a positionoutside the nut is to progressively equalize R1 and R2. See FIG. 10,from which it can be seen that the difference between R1 and R2 isgreater than between S1 and S2.

If the point of cutting of the axes is then moved further and furtheraway then it is possible to use any shape of thread form in this device.

The force required to disengage the nut is approximately proportional tothe load supported by the nut.

The instrument shown in FIGS. 11 to is a sledge microtome constructed intwo main parts, a sledge portion 1 of box like form with open ends andhaving flanges 2 upon which the sledge. portion rests upon slideways 3along the inner surface of the slides 4 of the box like base of theapparatus.

The slidable sledge portion 1 carries upon its upper surface 5 a knob 6,by means of which the sledge is movable back and forth upon theslideways 3 of the box like base. There is also provided on the uppersurface 5 a specimen holder 7, which holds a specimen 8 by means of theclamp 9. As the specimen 8 moves along, a thin section is cut by theknife 10.

On the forward stroke the specimen holder 7 is raised by a pawl 11operating against and turning a toothed wheel 12, the extent ofengagement being controlled by the knob 13, while the lever 26 controlsthe extent of movement of the pawl 11 on its return stroke. By thismeans the thickness of the section of the specimen is controlled.

Rotation of the toothed wheel 12 rotates the disengageable nut 14,constructed in accordance with the invention, along a lead screw 15. Thenut 14 is associated with the specimen table 7, and slides it in thegrooves 16 to adjust its height.

By rotation of the lever 17 in an anti-clockwise direction, twofunctions are performed. Firstly push rod 18 attached to the nut 14 ismoved downwards against the action of a spring 19 thus tilting the nut14 from the lead screw 15, in accordance with the invention. The nutthereby becomes disengaged, from the lead screw, for rapid movementthere along. Simultaneously with this release the block 20 is moved toengage gears 21 and 22 which are nonnally disengaged.

A few turns of the knob 23 moves the nut 14 and hence the specimenholder 7, from one end of the lead screw 15 to the other or to anyintermediate position. When the lever 17 is returned to its originalposition the reverse function takes place, and the nut 14 becomesengaged with the lead screw 15 and is held there by the spring 19.

It may be clearly seen from the above description that when the nut 14is engaged with the lead screw 15 the specimen holder 7 is raised aconstant and adjustable distance each time the sledge portion of theapparatus is reciprocated by means of the knob 6, but when the nut 14 isdisengaged from the lead screw 15, the specimen holder 7 moves up anddown in an uninterrupted manner by means of the knob 23. By this meansthe appropriate relative levels between the specimen and the knife canbe obtained at the commencement of a run of cuts preparatory to theengagement of the nut 14 and lead screw and the cutting of a run ofequal thickness specimens obtained.

The upper lever 24 operates the pawl 25, by means of which the specimentable 7 may be lifted step by step in fine stages without the necessityof sliding the table each time. i

It is to be understood that the above description is by way of exampleonly and that details for carrying the invention into effect may bevaried without departing from the scope of the invention.

I claim 1. In combination with a precision instrument, an adjustingmechanism comprising an externally threaded fine adjusting screwrotatable about its longitudinal axis, a nut having at least a partiallythreaded bore interengaging with said screw through which an axial forcemay be transmitted to said nut upon rotation of said screw, said nutincluding a smooth bore having a diameter larger than the diameter ofsaid screw extending therethrough at an angle to said partially threadedbore and having an axis which intersects the axis of said partiallythreaded bore at substantially the midpoint thereof, means for rotatingsaid nut about a tilting axis extending through said point ofintersection and perpendicular to the axis of said screw for selectivelyaligning said screw with either said partially threaded bore or saidsmooth bore, whereby said nut may be slid axially over said screw whensaid smooth bore is aligned with said nut and said nut may be translatedrelative to said screw upon rotation thereof when said partiallythreaded bore is aligned with said screw, the resultant of the forcetransmitted by said screw to said nut upon rotation of said screwpassing through said tilting axis.

2. The combination of claim 1 wherein said adjusting screw is disposedvertically.

3. The combination of claim 1 wherein said precision instrument is asledge microtome.

i i i

1. In combination with a precision instrument, an adjusting mechanismcomprising an externally threaded fine adjusting screw rotatable aboutits longitudinal axis, a nut having at least a partially threaded boreinterengaging with said screw through which an axial force may betransmitted to said nut upon rotation of said screw, said nut includinga smooth bore having a diameter larger than the diameter of said screwextending therethrough at an angle to said partially threaded bore andhaving an axis which intersects the axis of said partially threaded boreat substantially the midpoint thereof, means for rotating said nut abouta tilting axis extending through said point of intersection andperpendicular to the axis of said screw for selectively aligning saidscrew with either said partially threaded bore or said smooth bore,whereby said nut may be slid axially over said screw when said smoothbore is aligned with said nut and said nut may be translated relative tosaid screw upon rotation thereof when said partially threaded bore isaligned with said screw, the resultant of the force transmitted by saidscrew to said nut upon rotation of said screw passing through saidtilting axis.
 2. The combination of claim 1 wherein said adjusting screwis disposed vertically.
 3. The combination of claim 1 wherein saidprecision instrument is a sledge microtome.